Many modalities, or methods, exist for the creation of images to be used in medical diagnosis and treatment. These modalities include radiography, or X-ray imaging, computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, mammography, nuclear medicine, positron emission tomography (PET), and other modalities. The images produced as a result of these modalities are carefully examined by specialists having advanced training, such as radiologists.
In recent years, digital technology has made possible a shift from hard copy distribution of medical images for examination to digital distribution. Digital distribution of medical images is typically performed by picture archiving and communications systems (PACS). PACS comprise computers or networks dedicated to the storage, retrieval, distribution, and presentation of medical images. The medical images are stored in a format such as the digital imaging and communications in medicine (DICOM) standard. The use of PACS has also enabled teleradiology, whereby a radiologist or other specialist may examine a medical image and associated patient data at an off-site location.